Optical module and optical system

ABSTRACT

An optical module has a lens holder into which a lens array with three lenses and a diaphragm, for example, is inserted. The lenses and the diaphragm are oriented by way of the geometrical shape thereof such that no further optical adjustment is required. The circuit carrier and the lens unit are adjusted via at least one permanently flexible or springy element which is disposed between the lens holder and the circuit carrier and presses the component-equipped area of the circuit carrier away from the lens holder and against at least one stop element that is in positive contact with the lens unit. In the novel optical module or optical system it is no longer necessary to take into account the thickness tolerance of the circuit carrier and possible adhesives in the tolerance chain of optical modules. The module and the system are particularly suitable interior or exterior zone applications in motor vehicles.

DESCRIPTION OPTICAL MODULE AND OPTICAL SYSTEM

The invention relates to an optical module with a rigid circuit carriercomprising a component-equipped area; an unpackaged semiconductorelement arranged by means of flip-chip technology on thecomponent-equipped area of the circuit carrier and a lens unit which isarranged on the side facing away from the component-equipped side of thecircuit carrier; with the circuit carrier featuring an opening throughwhich electromagnetic radiation is projected from the lens unit onto thesemiconductor element; and with the lens unit comprising a lens holderand a lens arrangement with at least one lens. Generic optical modulesare known for example from DE 196 51 260 A1.

The invention further relates to an optical system with such an opticalmodule.

Generic optical modules and systems are used especially in automotivetechnology. In such cases operation can be with electromagneticradiation from different frequency ranges, in which case cumulatively tothe visible light, with which applications in the exterior area of amotor vehicle typically operate, such as LDW (Lane Departure Warning),BSD (Blind Spot Detection), or (Rear View Cameras), the infrared lightwhich is invisible to the human eye is preferred for applications in theinterior of the motor vehicle such as OOP (Out of Position Detection) orfor additional outside illumination of a night vision system.

High demands are imposed on applications in the interior and exteriorarea of a vehicle as a result of external influences such astemperature, moisture, contamination and vibration. The typical lifetimefor systems in the motor vehicle is around 10 to 15 years, with onlyextremely low failure rates being tolerated, so that the components ofan optical system of the type mentioned at the start may only exhibitvery slow ageing.

Since in many cases the space for installing optical modules or opticalsystems is very restricted, additional difficulties arise inimplementing the optical systems. It is thus extremely difficult usingconventional means to construct a hermetically sealed reliable unitconsisting of a camera chip (currently CCD or CMOS sensors) and optics.

Thus with these types of systems, with which images or similarinformation are recorded, it is obviously necessary for the optics tohave their precise focus at the point at which light is converted intoinformation (e.g. film plane, optical surface of CCD or CMOS sensor).The distance between the camera chip and the optics must thereforeeither be basically set and fixed once during manufacturing, or thefocus is reset for each image (focusing on object, non-concretive rays).This makes such units very expensive to manufacture. Furthermore aquality risk arises as a result.

However cameras for specific low-cost applications such as automotive,industry, digital cameras, mobiles, toys etc. should be manufacturedwhere possible, as regards cost and quality assurance aspects, withoutadjustment procedures between optics and camera chip, that is withoutmaking adjustments to the focus on the optical surface of the CMOS orCCD sensor. This basically conflicts with the stated requirements.

One possibility for developing a focus-free system is to reduce the sumsof the possible tolerances and elements, so that the module or systemfunctions as a result of the design without adjustment in at least onespecific distance and temperature range. Where the invention is used forexample within the framework of an occupant protection system of a motorvehicle, to which the present invention is however not restricted,sharper images at distances of for example 15 cm to 130 cm as well as attemperatures of for example −40° C. to +105° C. should be able to beguaranteed. The fewer elements are included in the tolerance chain, theeasier this is to implement. A major proportion of the tolerance chainis taken up by the circuit carrier for the camera chip (e.g. CCD orCMOS). Thus for example by using very thin, so-called flexible circuitboards, an attempt is made to include only a very small thicknesstolerance. In addition the required solder and if necessary gluedconnections or such like between the chip and the circuit carrierconstitute a large element in the tolerance chain.

Using only one lens avoids additional optical tolerances being caused bya complicated lens construction. The lens holder, which is preferablymade of plastic and can itself be linked to the lens arrangement in adifferent way so that an exact optical alignment of the lens arrangementand of the semiconductor element in relation to the lens holder or thelens arrangement respectively can always be ensured.

However with systems which largely feature a classical layout consistingof lens and camera chip, with the camera chip being accommodatedunpackaged as what is referred to as a flip-chip on a suitable circuitcarrier, it is difficult to get around the given overall problems andsimultaneously meet the given quality requirements. The lens itself musthowever be adjusted to the camera chip and feature a defined focusing.This is done by suitable fixing options, for example by screwing, gluingor such like, by means of which the lens is fixed relative to the camerachip to the opposite side of the circuit carrier from thecomponent-equipped surface so that the circuit carrier as well as theadhesive or the screw connection or such like are disadvantageouslyincluded in the tolerance chain.

The object of the invention is to make available an optical module andan optical system with a semiconductor element arranged on a rigidcircuit carrier in which the thickness tolerance of the necessarycircuit carrier and look connections possibly required or suchlike arelargely eliminated so that with a simple and cost-effective assembly, areliable optical quality without adjustment and especially focusingeffort can be provided and can be maintained over the lifetime of themodule or system.

This object is achieved with the features of the independent claims.Advantageous embodiments of the invention, which can be usedindividually or in combination with each other, are specified in thedependent claims.

The invention builds on the generic optical module such that between thelens holder and the circuit carrier at least one permanently flexible orspringy element is arranged which presses the component-equipped area ofthe circuit carrier away from the lens holder against at least one stopelement that is in positive contact with the lens unit.

Unlike the solutions known from the prior art in which the circuitcarrier is pressed against a lens holder, the present invention followsa new path whereby the circuit carrier is pressed in the oppositedirection by a permanently flexible element, i.e. away from lens holder,and a stop there makes positive contact with the optics. In this way theentire tolerance of the circuit carrier and possible adhesives are notonly largely but advantageously completely eliminated. Thus with thepresent invention a manufacturing technology with especially lowtolerances between an unpackaged semiconductor element and a lens unitis made possible.

For example the positive contact is implemented by a positive-contactsurface embodied on the stop element. In a first development, this canbe part of a snap-on connection. To this end the stop element ispreferably implemented by a hook embodied on the lens holder. This notonly makes the assembly, but also subsequent recycling, especially thedisassembly of optics and electronics, especially environmentallyfriendly and simple.

In an alternative development the stop element is part of a screwed orriveted connection or such like, with the stop element preferably beingimplemented by distance bolts or screw holes arranged on the lens holderwhich operate in conjunction with a screw, a plastic rivet for exampleor such like.

In accordance with the invention the permanently flexible or springyelement is preferably rectangular in shape or annular in shape or suchlike, preferably embodied as a punched part. This advantageously allowsthe part to be mass produced.

For example permanently flexible or springy elements made fromthermoplastic elastomers (TPE), Silicon or such like have proventhemselves which preferably simultaneously seal the lens unit againstthe circuit carrier, especially to protect it against moisture and/ordust etc. In an especially advantageous manner the inventive opticalmodule can be developed by providing a ventilation channel in theconnection area between the rigid circuit board and the permanentlyflexible or springy element. This enables a sealed module to “breathe”,especially in the event of large variations in temperature. In theembodiment of the present invention with a permanently flexible orspringy element it is possible in a simple manner to incorporate aventilation channel into the element itself for example. If the opticalmodule is to be used where temperatures vary widely, it can provesensible to glue an adhesive pressure equalization element or pressureequalization foil over an opening embodied in a flexible element, ifnecessary also in the lens holder itself.

Alternatively or cumulatively porous, permanently flexible or springyelements, especially embodied in foam rubber are of advantage, by meansof which “breathing” of the lens can be implemented.

The invention finally consists of an optical system with an opticalmodule of the type given above. In this way the advantages of theoptical module can also be brought to bear within the framework of anoverall system.

The invention is based on the knowledge that, unlike previous approachesto the solution, it is possible to press the circuit carrier by means ofa permanently flexible or springy element in the opposite direction,i.e. away from the lens holder and against a stop which is in positivecontact with the optics, so that a compact highly-integrated modulesolution with small dimensions is available and which at the same timeis simple to assemble and to disassemble and is thereby especiallycost-effective.

The optical module and the optical system are practicallymaintenance-free. Especially in the sense of cost saving it is also afact that no optical adjustment of the optical module is required sincethis is provided in any event by the geometric design of the stopelements, in which case the tolerance chain is shortened by eliminatingthe circuit carrier and adhesive tolerance by a further amount. Only thetolerance of the stop element remains in the tolerance chain. Thisamount is however tool-associated. The optical module in accordance withthe invention or the optical system is thus far better than previouslyknown modules in respect of tolerances.

The invention can be employed especially usefully in the implementationof video systems, if necessary in combination with radar systems,ultrasound systems or such like in the automotive area.

The invention is now explained with reference to the accompanyingdrawings on the basis of preferred embodiments.

The figures show schematic diagrams of:

FIG. 1 a perspective part cross-sectional diagram of an inventiveoptical module;

FIG. 2 a side view of the inventive optical module from FIG. 1;

FIG. 3 the lens holder of an optical module in accordance with theinvention with screw holes;

FIG. 4 the lens holder in accordance with FIG. 3 with a permanentlyflexible or springy annular element placed on it or formed into it;

FIG. 5 the lens holder in accordance with FIG. 3 or 4 with apre-positioned circuit carrier;

FIG. 6 the lens holder in accordance with FIG. 5 with a fixed circuitcarrier;

FIG. 7 a sectional diagram through the optical axis of an optical modulein accordance with the invention; and

FIG. 8 a diagram of an optical module in accordance with the inventionshowing a cross section through the fixing.

In the description of the preferred embodiment of the present inventionbelow the same reference symbols refer to the same or comparablecomponents.

A lens unit 14; 16, 18, 20; 21 and a rigid circuit board 10, comprisinga component-equipped area 10 a can be seen in the assembled state of theoptical module shown in FIG. 1 and 2. The rigidly embodied circuit board10 shown forms the circuit carrier 10 for an unpackaged semiconductorelement 12 sensitive to electromagnetic radiation, which is accommodatedhere as a flip chip 12, which has the advantage that there are noadditional tolerances within the sensor or component (e.g. carrier chip,adhesive, etc.). The rigidly embodied circuit board 10 shown here is ineffective contact with a ribbon cable or a flexible circuit board 27,with solder pads 28 being provided at the opposite ends of said cable,so that an electrical contact between the optical module and a circuitboard (not shown), for example by iron soldering using the solder pads28, can be established.

The semiconductor element 12 is disposed on the circuit carrier 10 viasolder bumps 30. The semiconductor element 12 is disposed by flip-chiptechnology on the circuit carrier 10. So that electromagnetic radiationcan reach the semiconductor element from the lens arrangement 16, 18,20; 21 arranged on the side of the circuit board 10 b facing away fromthe component-equipped area 10 a of the circuit carrier 10, the rigidcircuit carrier 10 features an opening 24. Likewise the permanentlyflexible or springy element 22 arranged between lens holder 14 andcircuit carrier 10 or its second surface 10 b has an opening 32. Throughthese openings electromagnetic radiation can reach a surface 34 of thesemiconductor element 12 sensitive to electromagnetic radiation.

The semiconductor element 12 can be designed in accordance with theprior art as a CMOS or CCD for example. A glued connection can also beused in addition to the solder connection 30. For strengthening anunderfill (not shown) can be applied. To protect the rear of theexpensive semiconductor element 12 against outside light radiationand/or environmental influences, a globtop 26 can be provided. To permitventilation of the optical module with temperature variations,especially strong ones, a groove (not shown) for ventilation can forexample be provided in the flexible element 22. Likewise it is possibleto arrange a glued pressure equalization element on an opening (notshown) in the flexible element 22 or in the lens holder 14.

Preferably a lens arrangement 14; 16, 18, 20; 21 with a number of lenses16, 18, 20 and if necessary at least one diaphragm 21 is provided in theform of a package. The optical quality can be improved by a lens with anumber of lenses, which is also possible within the framework of thepresent invention, especially since it is possible to work with finetolerances here. The lenses 16, 18, 20 and the diaphragm 21 are formedso that they assume a defined position relative to one another withinthe lens holder 14. Furthermore at least one of the lenses 20 isdesigned so that this lens 20 (as for example shown in FIG. 7 and 8)operates via locking means 38 in conjunction with the lens holder 14 andthus also assumes a defined position in relation to the lens holder 14and finally in relation to a semiconductor element 12. In this way alllenses 16, 18, 20 or diaphragms 21 are adjusted in relation to thesemiconductor element 12.

The circuit carrier 10 and lens unit 14; 16, 18, 20; 21 are adjusted inaccordance with the invention using the at least one permanentlyflexible or springy element 22 between lens holder 14 and circuitcarrier 10, which presses the component-equipped area 10 a of thecircuit carrier 10 away from the lens holder 14 against at least onestop element 13; 35, which is in positive contact with the lens unit 14;16, 18, 20; 21.

Preferably a surface to make the positive contact 37 is formed for thispurpose in the stop element 33; 35.

In the exemplary embodiment in accordance with FIG. 1 and 2 the stopelement 13 is for example part of a snap-in connection, which isimplemented by a hook arranged on the lens holder 14. Saidpositive-contact surface 37 is embodied on the hook 13 such that thecomponent-equipped surface 10 a lies against this surface 37.

FIG. 3 shows an alternate exemplary embodiment in accordance with theinvention. In this case the stop element 35 is part of a screwed orriveted connection, with spacer elements 35 being arranged on the lensholder 14 as a screw hole.

FIG. 4 shows the lens holder 14 in accordance with FIG. 3 with anannular permanently flexible or springy element 22 being arranged on it.Depending on choice of material, the element 22 can also be formed forexample by means of a two-component injection process or such like onthe lens holder 14. It can be clearly seen how positive-contact surfaces37 are formed on the end of the screw holes 35 facing away from the lensunit, the function is which is described below.

FIG. 5 shows the lens holder 14 in accordance with FIG. 3 or 4 with apre-positioned rigid PCB circuit carrier 10, with this carrier 10 notyet making positive contact with the positive-contact surfaces 37 of thespacer elements 35. In other words—the circuit carrier 10 is not yetpushed downwards over the system onto the permanently flexible element22.

FIG. 6 shows the lens holder 14 in accordance with FIG. 5 with a fixedPCB circuit carrier 10. Fixing elements such as screws 33, plasticrivets or similar elements are inserted into the spacer elements 35until these fixing elements rest on the positive-contact surface 37. Inthis way the flip-chip surface or component-equipped surface 10 a of thePCB circuit carrier is aligned in a defined way for the circuit carrier10.

FIG. 7 shows this in a diagram with a cross section through the opticalaxis and FIG. 8 in a diagram with a cross section through the fixing ofthe optical module in accordance with the invention. It can be clearlyseen how the permanently flexible or springy element 22 presses thecomponent-equipped surface 10 a of the circuit carrier 10 against thefixing elements 33. In the prior art the circuit carrier has previouslybeen pressed against a lens holder. The present invention now follows anew path whereby the circuit carrier is pressed by means of apermanently flexible or springy element 22 in the opposite direction,i.e. away from the lens holder 14 and a stop 13; 33, 35 there makespositive contact with the optics. In this way the entire tolerance ofthe circuit carrier 10 and possible adhesives are completely eliminated.

The present invention starts with an optical module with a lens unitwhich comprises a lens holder 14 in which a lens arrangement consistingfor example of three lenses 16, 18, 20 and a diaphragm 21 is employed.Preferably the lenses 16, 18, 20 and the diaphragm 21 are uniquelyaligned to each other and in relation to the lens holder 14 by theirgeometrical design so that no further optical adjustment of the opticalmodule is necessary. The lens holder 14 is further connected via atleast one stop element 13: 35 embodied on the lens holder 14 with thecomponent-equipped area 10 a of a rigidly embodied circuit board 10which simultaneously acts as a circuit carrier for an unpackagedsemiconductor element 12 sensitive to electromagnetic radiation so thatfor the first time the thickness tolerance of the circuit carrier 10 andany glued connections advantageously is not included in the tolerancechain of generic optical modules or systems. Since in accordance withthe invention the semiconductor element 12 is arranged at a definedposition in relation to the other optical elements, i.e. especially thelenses 16, 18, 20 or the diaphragm 21, the type of circuit carrier 10,e.g. FR4, CEM, etc. . . . , no longer has to be fixed, as has previouslybeen the case. Instead “normal”, non-critical and thereby cheapercircuit carriers can be used.

The features of the invention disclosed in this description, in thedrawings and in the claims can be of importance both individually and inany combination for implementing the invention. They are especiallysuitable for applications in the interior or exterior area of a motorvehicle.

1-11. (canceled) 12: An optical module, comprising: a rigid circuit carrier formed with a component-equipped surface and an opposite surface; a non-packaged semiconductor element flip-chip-mounted on said component-equipped surface; a lens unit disposed on said opposite surface of said circuit carrier, said lens unit including a lens holder and a lens assembly with at least one lens; said circuit carrier having an opening formed therein for projecting therethrough electromagnetic radiation from said lens unit onto said semiconductor element; at least one permanently flexible or springy element disposed between said lens holder and said circuit carrier for biassing said component-equipped surface of said circuit carrier away from said lens holder and against at least one stop element forming a form-lock relationship with said lens unit. 13: The optical module according to claim 12, wherein said form-lock relationship is defined by positive-contact surface embodied on said stop element (13; 35). 14: The optical module according to claim 12, wherein said stop element forms part of a snap-on connection. 15: The optical module according to claim 14, wherein said stop element is formed by hooks disposed on said lens holder. 16: The optical module according to claim 12, wherein said stop element forms a part of a screw or rivet connection. 17: The optical module according to claim 16, wherein said stop element includes spacer bolts on said lens holder. 18: The optical module according to claim 16, wherein said stop element includes screw holes formed in said lens holder. 19: The optical module according to claim 12, wherein said permanently flexible or springy element has a rectangular or annular shape. 20: The optical module according to claim 19, wherein said permanently flexible or springy element is a punched part. 21: The optical module according to claim 12, wherein said permanently flexible or springy element contains thermoplastic elastomers (TPE) or silicon. 22: The optical module according to claim 12, wherein said permanently flexible or springy element is configured to seal said lens unit against said circuit carrier. 23: The optical module according to claim 12, wherein said permanently flexible or springy element is a porous sealing element. 24: The optical module according to claim 13, wherein said permanently flexible or springy element is formed of foam rubber. 25: An optical system, comprising at least one optical module according to claim
 12. 